DIFFUSION OF ANESTHETIC-GASES THROUGH DIFFERENT POLYMERS

Background. Improvement of working conditions and anaesthesia with clo sed systems includes reduction of gas leaks during anaesthesia. One so urce of contamination is the permeation of gases through plastic mater ials. The volume of gas permeating through a polymer depends on its mo lecular structure, the solubility and the diffusion coefficient. Metho ds. We designed an experimental set-up to measure the permeation rates of nitrous oxide, enflurane and isoflurane through components of the anaesthetic ventilator made of silicone, latex, rubber and polyvinylch loride (PVC). Reservoir bags, ventilation tubes and endotracheal tubes were investigated. Results. The highest permeation rates of anaesthet ic gases were observed with silicone materials. Permeation through sil icone exceeded that of the least permeable material by more than 10.00 0 times. By summarizing the permeation rates of the single items, the use of silicone increases the anaesthetic system's leakage rate by 4 m l/min, which means an increase of 18% in a modem anaesthetic ventilato r and of 31% in a closed system. Conclusions. The highest permeation r ates were found for nitrous oxide through silicone, although nitrous o xide has a known low solubility in plastic materials. The result demon strates the dependency of the leakage rate on the diffusibility. The l eakage of anaesthetic gases caused by silicone items does not alone le ad to unacceptable pollution of operating theatres. To minimize the to tal leakage rates of minimal-flow-systems however, plastic materials w ith low solubility and low diffusion coefficients have to be used.